Dysregulation of high-density lipoprotein (HDL) turnover or function may contribute to the excess atherosclerosis in individuals with insulin-resistant (type 2) diabetes and metabolic syndrome. These conditions are characterized by low HDL. However, it is unknown how insulin regulates HDL in normal physiology, or in the pathophysiology of diabetes. FoxO1 is an insulin-repressible transcription factor that has emerged as a key mediator of insulin signaling in liver and the vessel wall. We have determined that FoxO1 regulates multiple genes critical for HDL metabolism and function, and mice lacking hepatic FoxO1 have alterations in HDL lipid and protein content. Thus, we propose that FoxO1 links insulin signaling and HDL. In Aim 1, we will investigate the hypothesis that FoxO1 regulates selective uptake of HDL-cholesterol in liver. We present preliminary data that FoxO1 regulates multiple steps in this process. In Aim 2, we will investigate the hypothesis that hepatic FoxO1 regulates macrophage-to-feces reverse cholesterol transport. We will determine the roles of individual HDL genes in the FoxO1 phenotype, and determine the effects on atherosclerosis. In Aim 3, we will investigate the hypothesis that FoxO1 regulates vasoprotective functions of HDL. We will examine the roles of FoxO1-regulated HDL components in endothelial barrier function and endothelial nitric oxide synthase activity. This work will build on novel hypotheses and a key mouse model to bring insight into the dysregulation of HDL during insulin resistance. The proposed studies will shed light on a key unanswered question in the pathophysiology of atherosclerosis, and reveal new targets for therapeutic intervention.